The present invention relates to a tap holder adapted for use in association with machine tools of various kinds, and more particularly, to a tap holder including a spring-loaded tap supporter whereby the tap is smoothly and effectively moved to cut internal threads in the workpiece. The tap supporter is spring-loaded such that an error likely to occur between the lead of the tap and the feed of the main spindle of the associated machine tool is automatically corrected.
It is known in the art that a tap holder is provided with a spring-loaded tap supporter whereby the tap is smoothly moved in the axial direction, commonly called "axial floating". The known tap supporter includes two coil springs coaxially overlaid wherein the outer coil spring works on the tap holding spindle when the spindle is advanced toward the workpiece whereas the inner coil spring works on the spindle when it is shrunk or withdrawn from the workpiece. In cutting internal threads the critical moment is when the tap is withdrawn. In order to enable the cutting face of the tap to be caught in the metal surface of the work, the inner coil spring must have a sufficient strength. However, owing to its inner location the diameter is restricted, and to compensate for it a greater number of windings will be needed, which necessarily leads to a prolonged length. As a whole the size and length of the tap holder become large. A large tap holder makes it difficult to be used in a restricted space or when holes are closely made in the workpiece. A more serious disadvantage is that a long tap holder is more liable to oscillation, which adversely affects the precision of the threads being cut.